1. Field of the Invention
The invention concerns a crescentless internal gear pump with an internally toothed internal gear, a pinion that meshes with the internal gear and a housing that accommodates the internal gear and pinion.
2. Description of the Related Art
This type of internal gear pump is known, for example, from EP 0 607 497 B1. The tooth heads of the hollow gear and the tooth heads of the pinion are each provided with a profile groove. A sealing element is inserted into the individual profile groove, which slides on the opposite tooth head of the pinion and internal gear during operation of the internal gear pump. The sealing element is provided with a channel that extends through the sealing element and makes a conducting connection between the base of the profile groove and the sealing surface of the sealing element. This ensures that the sealing element acquires the pressure necessary to force the sealing element against the opposite tooth head before the dead point is reached. After passing the dead point, however, the entire working pressure generated by the pump is not on the sealing element, but only a partial pressure.
Internal gear pumps with such sealing elements have proven themselves in principle.
The cited sealing elements are slightly moveable in the profile groove in the radial direction. The outer surface of each sealing element necessarily forms a gap with the inner surface of the profile groove. Control oil reaches this gap from the pressure side of a tooth head with the inserted sealing element in the internal space of the profile groove, i.e., the profile groove base. There the control oil enters the channel that passes through the sealing element in order to emerge again on the sealing surface of the sealing element in the region of the opposite tooth of the pinion or internal gear.
It has been shown that, despite the channel that passes through the sealing element, control of oil flow and thus the pressure with which the sealing element is forced against the opposite tooth head is not optimal. Especially at high pressures, for example at pressures of 250 bar, fluctuations in pressure force occur. These fluctuations are disadvantageous, especially with reference to the sealing effect between the sealing element, on the one hand, and the opposite tooth, on the other, and thus the efficiency and operating method of the entire internal gear pump is less than optimal.